Piezoelectric bimorph driven tuners for electron discharge devices



NOV. 11, 1969 w, H PER ET AL 3,478,246

PIEZOELECTRIC BIMORPH DRIVEN TUNERS FOR ELECTRON DISCHARGE DEVICES FiledMay 5, 196'. 3 Sheets-Sheet l I v I z z /5/2 I 32 I! a ,3

INVENTORS.

kW/Wm Nov. 11, 1969 w. H. PERKINS ET PIEZOELECTRIC BIMORPH DRIVEN TUNERSFOR ELECTRON DISCHARGE DEVICES 3 Sheets-Sheet 2 Filed May 5, 1967 wan Wm E W M Y B 2 7 6 Jv v u m. I

NOV. 11, 1969 w H PERKlNs ET AL 3,478,246

PIEZOELEGTRIC BIMORPH DRIVEN TUNERS FOR ELECTRON DISCHARGE DEVICES FiledMay 5, 196'? 3 Sheets-Sheet 5 I :POSIUOA/ER ATTOAA/EY United StatesPatent US. Cl. 315-39.55 14 Claims ABSTRACT OF THE DISCLOSURE Apiezoelectric bimorph is utilized to position a movable cavity wall. Thebimorph is Capable of'positiomng the cavity wall as a function of themagnitude of a control voltage applied across the bimorph. In oneexample the microwave cavity is a resonant cavity found within anelectron discharge device, and the cavity, including the positionablewall, forms the microwave turner therefore for tuning the electrondischarge device and especially for sweep tuning thereof. Further,the'bimorph is capable of generating a position representative trackingvoltage for representing the instantaneousfrequency to which themicrowave cavity is tuned.

This invention relates to microwave tuners, and more particularly, to amicrowave tuner for a magnetron in which a movable wall is used to tunea microwave cavity to different resonant frequencies.

A microwave cavity; a cavity including conductive walls, possesseselectrical properties similar to the conventional tuned circuitconsisting of an inductance and a capacitance at low radio frequencies.At very high radio frequencies or microwave frequencies, a conductivelywalled enclosure or cavity possesses the familiar characteristics ofresonance and impedance. With any, given cavity, the frequency withwhich resonance occurs is primarily a function of cavity size or volume.Hence, as is known, a microwave tuner may be constructed with a cavityutilizing a movable wall therewith that is adjustably positionablerelative to the other cavity Walls so as to increase or decrease theeffective size of the cavity, lowering or raising the frequency at whichthe cavity is in resonance.

Various types of mechanicaldevices are provided in the prior art forpositioning the movable cavity wall, including rods, and screws, whichmay be driven'by mechanical pneumatic or electromechanical arrangements.

Other devices are found inthe prior art which adjust or change theeffective resonance characteristics of -a micro- F wave cavity otherthan by the mechanical movement of one of the cavity walls. As anexample, tuners are constructed utilizing conductive or dielectric rodsor strips fixedly placed within the cavity or adjustably positionedwithin the cavity by a screw or slot and screw arrangement. v I

Additionally, ferroelectric devices are utilized as a tuner for amicrowave cavity. In that instance, with a ferroelectric tuning device,the effective capacitance of the included ferroelectric; hence, theimpedance of the microwave cavity, is adjustable with adjustment in thelevel of the voltage applied to the ferroelectric. In like manner,ferromagnetic or garnets are utilized astuners for microwave cavities.

Electron dischargqdevices.operable in the microwave frequencyregion,such as the klystron and magnetron, contain tunable cavities foradjustingthe output frequency of the device. Such tunable cavities areused for setting the electron discharge device to the desired frequencyand to modulate the frequency of the electron discharge device forjamming radar stations, in addition to, otherinore exotic applicationsof a modulated or swept signal. :1. The coaxial magnetron is one type ofelectron discharge device in which a resonant cavity of simplegeorntryhaving a movable wall is adjusted in size to' change the frerquency at which the device oscillates. In a coaxial'rnagnetron, theouter surface of the anode is surrounded by a single resonant cavity,which might be' considered donut shaped, which is designed to supportthe existence of the TE circular electrical mode of oscillation in amanner adequately described in any standard text on microwave tubes.After oscillation commences, the existence of the TE mode provides amagneticfield at all points about the outer surfaces of the anode withinthe resonant cavitywhich is in the same electricaltime phase; This inphase magnetic field'is admitted into alternate anode resonators,resonators commonly formed of slots or vanes, through coupling slotsthrough theanode between alternate anode resonators and the outer cavityresonator. The anode resonators not coupled to the resonant cavity havevoltages induced therein by the magnetic field introduced within thecoupled anode resonators. These induced voltages are out of phase withthe voltages in the coupled anode resonators, and thus adjacent anoderesonators alternate in electrical phase by 180, a condition necessaryto ensure the generation of the well known .1r mode of oscillation andthe resulting frequency thereof. In conventional magnetrons, this fixingof the Ir mode may be accomplished by a special anode, such as therising sun anode, or with conventional anode strapping. Of practicaladvantage, the coaxial magnetron possesses greater mode stability and alesser probability of starting oscilla tion ina mode other than the 1rmode.

Because the coaxial magnetron possesses a single resonant output cavityof a large size relative to the size of the anode resonators, theresonant output cavity stores a large amount of microwave energyrelative to the smaller anode resonators. Therefore, the cavityresonator is advantageously utilized for frequency control or tuning ofthe coaxial magnetron. As is evident from the simple construction of aconductivelywalled cavity of a coaxial magnetron, relatively simpletypes of devices, such as a movable washer shaped wall, can be utilizedto tune this type of magnetron than the more complicated tuners usedwith the ordinary magnetron. Other microwave tubes, such as theklystron, contain resonantcavity structures of relatively simplegeometry and also use the aforesaid relatively uncomplicated means oftuning to advantage. e However, the use of a movable wall to vary thefrequency of resonance of a microwave cavity within a microwave tube,such as the coaxial magnetron, possesses some practical disadvantage.Since a. plunger or, rod mus t,.-be

connected to the movable wall within thecoaxial magne For instance, US.Patent No. 3,032,680 to H. Olson;

reveals the large number .ofancillary mechanical parts utilized andlocated within the evacuated space, of (the magnetron in order toprovide .the simple movement of.

the cavity wall.

In addition to the foregoing disadvantages, a mea chanically actuatedmovement for moving a cavity w ll is relatively slow. Tuning atrelatively rapid rates, of above 500 or 3,000 cycles, such as is usefulwith frequency modulation or sweeping of a magnetron through a band offrequencies, is not practically possible. As is apparent, the morerapidly a change in tuning can be effected, the more versatile is themicrowave tuner and the electron discharge device within which it isembodied.

To obtain rapidly tunable tuner suitable for electron discharge device,various schemes are utilized. 'Ihis rapid sweeping is commonly termeddithering. Means to eifect dithering include a rapid periodical changein the magnetron anode voltages within the limits for which oscillationexists, a magnetically operated plunger which is moved back and forthwithin the evacuated space of the magnetron by a changing magnetic fieldcoupled from the outside into the magnetron and rapid periodical changein the size of cavities. These methods are, however, effective over asmall bandwidth of frequencies. Although some of these schemes permitsome fast sweep rates in tuning, they do not provide the largebandwidths desirable.

A proposal for a purely electronic tuner theoretically capable of fastsweep rates with no movable parts is advanced by M. G. Kroger in U.S.Patent No. 2,752,495.

A ferroelectric device is placed within at least one of the anoderesonators of a magnetron and exposed directly to the microwave field.In accordance with the teachings of that proposal, the ferroelectricdevice changes its dielectric constant, and hence, its effectivecapacitance as a function of the voltage applied thereacross.

Problems presented by the use of a relatively lossy ceramic, such as theferroelectric material therein utilized, render this alternativeimpractical in a high powered magnetron. Such problems have neither beenpresented nor disclosed in the U.S. Patent No. 2,752,495. For example,at any significant power the microwaves appearing within a microwavecavity heat a relatively lossy ceramic, such as the ferroelectricmaterial exposed to the fields within the cavity, causing it todecompose and contaminate the vacuum within the magnetron. Moreover, insome manufacturing procedures, a magnetron is subjected to very hightemperatures and this presents the same aforementioned problems.

In addition to tuners, a further consideration of importance withtunable microwave cavities, and hence, to tunable magnetrons in manyapplications in the utilization of some means to obtain a signalrepresentative of the frequency at which the magnetron is operating;because a magnetron, in many instances, operates at frequencies inexcess of 10,000 mHz. Various means to directly measure or indicate thefrequency at which the magnetron is operating are relatively expensive,and as a practical matter, unavailable.

With some of the tuners of the prior art, for example, those utilizing amovable wall driven by a plunger or rod, complicated servo mechanismsare included which directly monitor the position of the plunger. Suchdevices are complex, expensive, and bulky. A simpler means of obtaininga signal representative of the movement of the cavity wall is obviouslydesirable.

Therefore it is an object of the invention to provide a rapid tunerwhich tunes a microwave cavity to different frequencies of resonance.

It is another object of the invention to provide an electricallyoperated microwave tuner for a magnetron, which mechanically moves acavity wall and which does not require movable members extending betweenthe exterior of the magnetron and the evacuated portions of themagnetron.

It is another object of the invention to provide a tuner within acoaxial magnetron having a mechanically movable wall that provides ahigh sweep rate of more than 50 Hz. and possible up to 1 mHz., by purelyelectrical actuation.

It is n na a ject 9f t e n n o o p d a rapid tuner for a magnetron whichis protected against the heated effect of direct radiation withmicrowave energy found within the magnetron.

It is still another object of the invention to provide a coaxialmagnetron rapidly tunable over a relatively large bandwidth withoutextending any movable parts between the inside evacuated portion of thetube and the exteror.

It is an additional object of the invention to provide a voltage signalrepresentative of the frequency to which the microwave tuner is tuned.

It is a further object of the invention to provide a means formonitoring the position and shape of a movable tuner wall within amicrowave cavity that is neither bulky in size or complex in itsconstruction.

In. accordance with the invention, a microwave cavity includes a movablewall. A piezoelectric bimorph device located outside the formedmicrowave cavity has one portion fixed to a support outside themicrowave cavity and, another portion connected with the movable cavitywall for creating mechanical movement of the wall in response to theapplication of voltage to the piezoelectric bimorph device. Thepiezoelectric bimorph device comprises at least a first and a secondlayer of piezoelectric material separated by a layer of conductivematerial, and conductive layers on the outer sides of the piezoelectriclayers affixed together to form a thin integral sandwich. Eachconductive layer is adapted for connection to a source of voltage.Preferably the two piezoelectric layers are oppositely electricallypoled.

Further in accordance with an additional feature of the invention,electrical leads connected across the second piezoelectric layer areutilized to convey voltages representative to the mechanical movement ofthe piezoelectric bimorph device which are generated by the secondpiezoelectric layer in response to mechanical stress created by thefirst piezoelectric layer.

The invention may be further characterized in that the cavity wall is ofa low mass, such as a conductive coating placed or deposited upon one ofthe layers of the piezoelectric bimorph device or a thin layer attachedthereto. Additionally, in accordance with the invention, a novel tunablecoaxial magnetron structure embodies the foregoing tuner to providerapid tuning or sweep rate.

The foregoing and other objects and advantages of the present inventionbecome apparent from a reading of the specification in view of thedrawings, in which:

FIGURE 1 is a partial view in section of a tunable coaxial magnetronembodying a piezoelectric bimorph actuator and tuner in which themovable cavity wall is deposited upon a piezoelectric layer;

FIGURE 2 is a partial view in section of another tunable coaxialmagnetron embodying a piezoelectric bimorph actuator and tuner in whichthe movable cavity wall is deposited upon a piezoelectric layer, and theactuator and tuner are mounted along the outer edge to a tubularsupport;

FIGURE 3 is a partial view in section of a third form of tunable coaxialmagnetron embodying a piezoelectric bimorph actuator and tuner in whichthe movable cavity wall is spaced from the actuator and mechanicallycoupled thereto along its outer periphery;

FIGURE 4 is a partial view in section of another tunable coaxialmagnetron embodying a piezoelectric bimorph actuator and tuner in whichthe movable wall is coupled to the actuator by rods and linkages;

FIGURE 5 is a partial view in section of another coaxial magnetronembodying a piezoelectric bimorph actuator and tuner in which theactuator is mounted exter nally of the evacuated regions of themagnetron, and the movable wall is connected to the actuator by abellows and rod arrangement; and,

FIGURE 6 is a partial view in section of a tunable co-. axial magnetronembodying a piazgelectrig bimorph 3Q:

tuator that is in turn adjustably positionable and carried by a priorart positioner, and in which the movable wall is positioned by both thepositioner and the actuator.

FIGURE 1 shows, in cross section, a partial view of a coaxial magnetronembodying one form of the invention. This includes an evacuated housingwhich includes a first cylindrical cup-like housing or body portion 1,containing grooves 2 for the installation of conventional cooling fins,not illustrated, a cylindrical wall portion having an inner cylindricalsurface or wall 3; a top washer shaped inner surface or wall 4; and asecond smaller cup-like body 5 attached along the cup rim to the firstcuplike body 1, by annular seals 6 and 7. A cylindrical jacket 8 is alsosealed to the side of the second cup-like body 5 to provide a more rigidstructure. A pole piece 9 is seated within the top of the secondcup-like body 5 by a flange portion 10 of the hole piece and partitionsthe two body portions of the magnetron housing. Pole piece 9 projectsabove its flange portion 10 into first cup-like housing portion 1 andprojects beyond wall 4.

Pole pieces 9 and 11 are conventionally constructed of ferromagneticmaterial and have their ends or tips facing each other across a gap toprovide a path for magnetic flux between the pole pieces across theinteraction region of the magnetron. Magnetic flux is coupled to thepole pieces from a source such as the conventional permanent magnet orelectromagnet, not illustrated, which is mounted to the body of themagnetron in the usual manner. Extending through a passage through polepiece 11 is a cylindrical cathode 12 of emissive material. A heater orfilament winding, not illustrated, for heating the cathode surfaces toenhance electron emission is conventionally included within the hollowpassage 13 through cathode 12. However, if desired, the cathode mayconsist of heater or filament windings coated with an electron emittingmaterial.

Concentrically surrounding and spaced from the cylindrical cathode is acylindrical anode 13 supported upon pole piece 9 which contains aplurality of anode resonators surrounding cathode 12 in the customarymanner. In the magnetron of this figure, each of the plurality of anoderesonators is formed in the small space, not illustrated, between eachof a plurality of spaced conductive vanes, such as vanes 14 and 15 whichare attached to the inner wall 16 of anode 13. These vanes are spacedsymmetrically about the inner wall 16 of anode 13 and project out frominner anode wall 16 to within a predetermined distance of cathode 12leaving a gap therebetween. The gap between the projecting tips or endsof the vanes andthe cathode is termed in the art as the interactionregion. In the illustrated section of FIGURE 1 only two nonadjacent onesof these vanes 14 and 15 are visible.

An outer resonant output or microwave cavity 17 surrounds the outer wall18 of anode 13. This cavity 17 is effectively formed between the topwasher shaped inner wall 4 of housing portion 1; the surrounding innerside wall 3 of housing portion 1; the outer wall 18 of cylindrical anode13; and a washer shaped conductive wall 29, which in this embodimentadditionally functions as an electrode of a washer shaped piezoelectricbimorph sandwich to form a donut-like shaped cavity. A plurality ofmicrowave energy passages or slots 19 extend through cylindrical anode13 to couple microwave energy between alternate ones of the anoderesonators and resonant output cavity 17. l v

A conventional microwave window 21, illustrated in part, is mounted in ahousing wall to couple microwave energy generated by the magnetron andappearing in the resonant output cavity 17 to external loads. The window21 may be constructed of material that passes microwave energy but whichis impervious to air, such as alumina.

A washer shaped or annular plate 22 surrounds an end of pole piece 9 andis fixedly mounted to the flange portion 10 of pole piece 9 by a flaredcylindrical support member 23, which contains a flat rim portion that isseated within a groove 24 of flange portion 10 to position plate 22within the chamber formed between the first cup like body portion 1 andpole piece 9 within the magnetron housing. Plate 22 is a nonconductivelossy ceramic to suppress undesired modes of microwave energy incidentthereon. In accordance with the present invention, there is mounted toplate 22 a piezoelectric bimorph sandwich 25,;previously referred to,which in order to conform to the.shape of the space between cylindricalinner wall 3 and cylindrical pole piece 9 is also washer-like in shape.In the embodiment shown, the washer shaped piezoelectric bimorphsandwich 25 comprises two thin layers of piezoelectric material 26 and27, a thin layer of conductive material 28 which separates layers 26 and27 and which forms the center electrode, and two thin layers ofconductive material 29 and 30 which form, respectively, the first andsecond outer electrodes. These elements are sandwiched together in athin integral assembly. One piezoelectric layer is electrically poled inone direction from the middle electrode and the other layer isoppositely poled. Alternatively both layers of piezoelectric materialmay be electrically poled in the same direction.

Plate 22, tubular support 23, and the piezoelectric bimor h sandwich 25are fastened together with rivets or bolts 31 that etxend through theaforesaid washer shaped elements about their outer peripheries. Thebolts are insulated from electrodes 28 and 30 of the bimorph bynonconductive washers which may be of alumina or by removing asurrounding portion of an electrode of the piezoelectric bimorph 25. Asis necessary, insulating sleeves may extend through these holes. Rivets31 contact the outer electrode 29. Plate 22 has its surface facingbimorph 25 recessed or slightly concave toward the center so as to leavesufficient clearance in which the bimorph sandwich 25 may be flexed.

Although the bimorph sandwich is illustrated as being supported alongthe outer rim, it is apparent that it may be fastened in place along theinner rim. In the latter instance, the plate 22 possesses a convexshaped outer surface to provide clearance in which to allow the free endof the piezoelectric sandwich to flex. The conductive movable wall 29 ofthe formed resonant output cavity 17 in FIGURE 1, in addition, functionsas one of the electrodes of the piezoelectric bimorph sandwich 25.

An electrical lead 20 is soldered to electrode 28 and extends through anopening in layer 26 of the piezoelectric bimorph sandwich 25, plate 22,flange 10, and second cup portion 5 of the housing. The lead 20 issupported by a glass bead 32 that insulated lead 20 from the housing andglass bead 32 is in turn supported by a flared tube 33 sealed to housingportion 5. Glass head 32, in addition, prevents leakage of air into theevacuated portions of the magnetron housing. Inserted in series withlead 20 is a flexible helical conductive spring 34 which allows lead 20to move with movement of the bimorph 25 while imposing little restraintthereon.

A second electrical lead 35 is connected to electrode 30 and extendsthrough an opening in plate 22, flange 10,.a glass bead 36 which in turnis supported by the flared tube 37. A third lead substantially identicalwith lead 20 may be soldered to the outer conductive electrode 29;however, because of the symmetry of the illustration, such lead would belocated behind lead 20 and would be entirely visible and, hence, is notillustrated. Structure substantially identical to that provided for lead20 would beprovided to connect such lead through to the exterior of thehousing. Since one of the electrodes, such as electrode 30, is normallyof ground polarity, in lieu of the aforementioned electrical lead toconnect such electrode to ground potential, a satisfactory groundconnection is obtained by using the magnetron housing which is normallyelectrically grounded. Such an electrical path exists between electrode29, rivets 31, support 23, and pole piece flange 10 to the metallichousing walls, Circuit connections for ground polarity are then made tothe housing or to conductive supports carrying the housing.

Electrical connections from a source of high voltage are made to thecathode 12 and from a source of filament voltage to the filamentwinding, not illustrated, are made through an electrical socket assemblymounted to the rear of the first body portion 1 of the magnetron. Suchsocket and assembly are conventional; for example, as disclosed in US.Patent 3,032,680, and is not herein illustrated. The anode 13 is bothphysically and electrically connected to portions of the magnetronhousing and is electrically grounded through the housing in theconventional manner to create an electric field between the anode andcathode. The magnetron is evacuated and otherwise assembled in anyconventional manner and the conventional magnets are mounted to thehousing in the conventional manner to create a magnetic field betweenthe pole pieces.

The theory of operation of a coaxial magnetron is conventional and isdescribed in the literature. In essence, under the interaction of thecrossed electric and magnetic fields, e.g., the electric field extendingbetween the cathode 12 and the surrounding anode 13 across theinteraction region, and the magnetic field extending axially between theends of pole pieces 9 and 11 within this same interaction region,potential energy from the electrons emitted from the cathode istransferred to an electromagnetic wave apparently traveling around theanode at a predetermined phase velocity. Oscillation builds up in theinteraction area generating R.F. fields in the anode vanes, then acrossthe slots which induce RF. fields in the outer cavity. Microwave energyin the form of a TE circular electric mode of oscillation is sustainedwithin the output cavity 17. This TE mode has a magnetic field H offixed phase extending around the outer wall 18 of anode 13. The couplingslots 19 couple this H-field from resonant output cavity 17 to alternateanode resonators which thus placed in the same phase. Each of the otheranode resonators, not so coupled to the output cavity, has voltagesinduced from the electromagnetic waves within the coupled anoderesonators and are 180 out of phase with those fields in the cavitycoupled resonators.

Thus, between any two adjacent anode resonators there exists a forced180 shift in electrical phase. This is the mode of oscillation commonlydenoted as the 1r mode since a magnetron is capable of operating in manydifferent modes, it is necessary to select and attempt to maintainoperation in only a single mode; desirably the 1r mode. The resonantoutput cavity 17 through the alternate anode resonator coupling tends tolock the magnetron in the 1r mode.

The microwave energy generated by the magnetron is transmitted from theresonant output cavity 17 through the microwave window 21 to anelectrical load or other microwave equipment. Because the resonantoutput cavity is so much larger than any of the individual anoderesonators, it stores a larger proportion of microwave energy andtherefore, has a much larger frequency determining effect on themagnetron. The frequency of oscillation of the coaxial magnetron is thusdetermined primarily by the size of the resonant output cavity; hence,the resonant output cavity is effectively tuned by adjusting theposition of movable wall 29.

A known effect exhibited by piezoelectric material is the expansion orcontraction of the material that occurs with increases or decreases ofvoltage applied across the material relative to the polarity exhibitedby the material. Utilizing this movement to move a microwave cavity wallprovides some degree of tuning. However, with a pure piezoelectricmaterial, the movement caused by the application of voltages is verysmall. The bimorph or piezoelectric sandwich type of piezoelectricdevice multiplies the effects produced with a homogeneous piezoelectricmass.

Piezoelectric bimorphs are commercially available elernents which areformed with two thin layers of barium titanate piezoelectric material. Athin brass shim serves as the middle conductor sandwiched between thetwo layers. The outer surfaces of the thin layers are coated or fired-onsilver which serves as the two outer conductors. Electrical leads arepressed against each of the conductive surfaces. The piezoelectriclayers are given an electrical polarity by applying a high D.C. voltageat elevated temperatures for several minutes across each layer. Tooppositely pole the piezoelectric layers, polarizing the voltage isapplied across each in an opposite direction.

Thereafter when voltages are applied across each layer of such asandwich in such polarity so as to cause one layer to expand and theother to contract, the sandwich bends or warps proportionally to themagnitude of the applied voltage in the same manner as a bi-metallicthermostat or switch material bends or warps proportionally withtemperatures. In the alternative, a voltage or source of sweep voltagemay be applied across the electrodes of only one of the piezoelectriclayers, which effects a lesser amount of bending. However, the stressproduced by the bending or flexure of that one layer causes the secondpiezoelectric layer to also bend and generate a voltage across itselectrodes proportionally in magnitude to the amount of such bending orflexure.

While the commercial construction of the piezoelectric bimorph isacceptable for use in evacuated microwave cavities or in microwave tubeswhich are evacuated solely with a vacuum pump with the tubeconstructions of FIGURE 1 and the other figures, other constructions ofthe piezoelectric means are desirable if the manufacturing process usedrequires heating the tubes to high temperatures during the vacuumpumping process.

It has been found advantageous to make the bimorph of the followingconstruction: A laminate is formed on each side of the two layers ofpiezoelectric material which includes a first thin layer, perhaps 500 A.of chromium oxide; a second thin layer of about the same thickness ofchrome; a third layer of perhaps .1 to .2 mill thickness of copper; anda fourth layer of .1 to .2 mill of gold. A thin sheet or layer ofmolybdenum, which has thermal expansion characteristics substantiallysimilar to the barium titanate piezoelectric material is placed betweenthe two piezoelectric layers. The piezoelectric layers and molybdenumsheet are then pressed together in a sandwich and exposed to a hightemperature causing diffusion of the gold resulting in an integralsandwich construction. These materials have low vapor pressures and donot boil off during the heating process encountered in theaforementioned tube assembly procedure. The outer gold layers form aportion of the outer conductors and the molybdenum forms the middleelectrode of the piezoelectric bimorph sandwich.

The movable wall 29 is thus moved or positioned by the bending flexingof the piezoelectric bimorph 25, integrally formed therewith in theembodiment of FIGURE 1, which bends or flexes as a function of thevoltage applied to the bimorph electrodes. Voltages from an alternatingvoltage source may be applied to the electrodes to cause the washershaped bimorph to flex back and forth, to increase or decrease theeffective size of surrounding resonant output cavity 17. Since thefrequencies at which the magnetron oscillates are normally very high,the small movement of wall 29 is sufficient to vary significantly thesize of the cavity relative to the wavelength of those microwavefrequencies.

Alternatively, a source of sweep voltage may be applied between only themiddle conductive layer or electrode 28 and one of the outer conductivelayers, such as electrode 29. This voltage causes the bimorph sandwishto flex back and forth to a lesser degree than is obtained with theprevious application of voltage to the outer electrodes to move themovable wall 29, and hence, vary the size of and frequency of resonanceof the microwave cavity. The second piezoelectric layer responds to thebending or flexing caused by the first piezoelectric layer by generatinga voltage which appears across the middle electrode 28 and the other oneof the outer electrodes 30, proportional in magnitude to the amountofbending or flexing. Therefore, this generated voltage is indicative ofthe frequency to which the microwave cavity or resonant output cavity 17is tuned, and is, in essence, a tracking voltage, Moreover stressescreated in the piezoelectric caused by-vibration or shock also induce atransducer output voltage proportional thereto. This, therefore providesa most accurate tracking signal. Connection of these electrodes tosuitable equipment responsive to tracking voltages may then be made.

FIGURE 2 shows many of the details of the magne; tron constructionutilized in FIGURE 1, and such details are similarly labeled. In thisembodiment, the washer shaped piezoelectric bimorph tuner 25, includinga first piezoelectric layer and a second piezoelectric layer '26 and 27sandwiched together with three conductive electrodes or layers 28, 29,and 30, is disposed within an annular chamber within the first cup-likebody portion 1 bordering the reasonant output cavity 17 in the spacebetween cylindrical anode ,13 and cylindrical wall 3. The outerconductive layer 29 in addition to its functions as an electrode ofbimorph 25 forms the movable wall of the annular resonant output cavity17.

A tubular support member 40 contains a bent over lip portion. Thistubular support member is sealed to a rim 41 surrounding the pole pieceflange 10, and is frictionally seated and brazed in place. A pluralityof holes through the outer rim of bimorph 25 and the lip portion ofsupport 40 contain bolts 42 that extend through some of these holes andfasten the bimorph to the tubular member 40. Other holes throughbimorph'25 and support 40 are provided for connection of electricalleads tothe electrodes of the bimorph. An insulator sleeve 43 is shownextending through such a hole and a smaller diameter conductive lead 44extends therethroug'h. Lead "44 is soldered to a coupling member 45 tomake conductive contact with the movable wall or outer conductive layer29 of the bimorph 25. A like electrical lead is connected with the inneror middle conductive layer 28 of the bimorph, but is not visible in thesectional view shown. Electrical lead 44 is connected to a largerdiameter electrical lead 45. Lead 45 extends to the magnetron exteriorthrough a glass bead 32 supported in an opening in the magnetron housingby a support member 33. Glassbead 32 both electrically insulates theelectrical lead from the housing walls and provides a seal to preventloss of the vacuum within the magnetron.

A third electrical connectionis made to electrode 30 through themagnetron housing which is always connected to an electrical ground.Such connection extends from electrode 30', tubular support member 40which abuts against the electrode," rim 41,'a'nd flange to the magnetronhousing walls. l

The washer shaped bimorph 25 in this figure is'fixed in position alongits outer rim and, therefore, in response to'the application of sweepvoltages across the electrodes is free to flex along the inner rim toshorten or" lengthen the size of resonant output cavity 17. One suchposition of flexure is illustrated in FIGURE 2 by dotted outline 46.

'FIGURE 3 shows an embodiment of the invention in which thepiezoelectricbimorphactuator 25 is coupled to a physically separatemovable 'wall to form the tuner. The discussion of conventional elementsof the coaxial magnetron discussed with respect to FIGURE 1 is notrepeated and reference is 'madeto that description,

FIGURE/3 shows the washer shaped piezoelectric bimorph actuator 25.Thisconsists of a first and second piezoelectric layer 26 and 27 ofpiezoelectric material such as barium titanate, a middleconductive layeror electrode 28, and two outer conductive layers or electrodes 29 and.30 forming an integral flexible thin sandwich. The dimensions of thesandwich, as is apparent, are exaggerated for purposes of illustration.This piezoelectric actuator is disposed within the chamber formedbetween the pole piece flange 10 and the walls of the first cup-likehousing portion 1 of the magnetron.

The movable wall 54 of cavity 17 consists of a thin metallic member ofwasher shape spaced from the body of the bimorph 25 and supportedthereby by an annular lip portion 55 which borders the space betweenmovable wall 54 and the bimorph 25. This lip portion 55 is constructedfrom a bent over portion physically integral with movable wall 54. Aminute groove 56 extends around the bend or juncture of this. lipportion with the movable wall in order to reduce restraint to flexure ofthe bimorph 25.

In FIGURE 3 a fixed washer shaped support plate50 is mounted to theflange portion 10 of pole piece 9 by tubular support member 51 mountedin a circular groove 52. in flange portion 10. Tubular support member 51is connected to the inner rim of support plate 50 bya plurality ofspaced bolts 53. The washer shaped piezoelectric bimorph actuator 25 ismounted along its inner periphery to support plate 50 by, for instance,the same bolts 53 that mount plate 50 to the tubular support 51. Thebolts 53 are suitably insulated from the electrodes 28, 29, and 30 ofthe bimorph actuator 25 as discussed with respect to FIGURE 1. Plate 50in this figure is convexly recessed to allow some clearance between theouter peripheral portions of the piezoelectric bimorph 25 and plate 50for permitting the flexure of the piezoelectric bimorph.

An electrical lead 57 is soldered to electrode 30, Lead 57 is connectedto a larger electrical lead 58 that extends through a passage in polepiece flange 10 and through a passage in a wall of the second cup-likehousing portion 5 to the exterior of the housing. Lead 58 is supportedin the housing wall by a glass bead 36 which insulates lead 58 whilepreventing air from entering the evacuated magnetron housing. Glass bead36 is supported by a flared tube 37, sealed to the housing wall.

A second electrical lead 59 is soldered to the middle electrode 28 ofthe piezoelectric bimorph actuator 25. A portion of piezoelectric layer26 and outer electrode 30 is cut away in order to allow lead 59 to haveconvenient access to the middle electrode 28. In turn, electrical lead59 is connected to alarger diameter electrical lead 60 in series with ahelical conductive spring 61. Helical spring 61 completes an electricalconnection to the bimorph electrode without posing a substantialmechanical restraint to the flexing or bending of the bimorph. Theelectrical lead 60 extends through a passage in the pole piece flangeportion 10 and through a passage in a wall of the second cup-likehousing portion 5. A glass bead 32 insulates the electrical lead 60 fromthe housing and maintains the vacuum within the magnetron housing. Glassbead 32.is supported by tubular support 33 which is sealed to thehousing wall.

A third electrical lead, having structure substantially identical withthat of electrical leads 59 and 60 is hidden behind the leads 59 and =60in the sectional view shown. That lead, not illustrated, provides anelectrical connection from the housing exterior to electrode 29 of thepiezoelectric bimorph actuator 25.

' In this embodiment, since the piezoelectric bimorph actuator 25 isfree to flex at the outer edges, the largest possible amount of movementis provided. This movement is coupled mechanically to the movable wall54 by lip portion 55 which causes the entire wall 54 to be moved as aunit for the largest possible distance. The manner and the theory ofoperation is the same as that discussed with respect to the embodimentof FIGURE 1.

1 FIGURE 4 shows an embodiment which has a rectangular shapedpiezoelectric bimorph linked or coupled at its middle with a movablewall of the resonant output cavity of a coaxial magnetron. Theconventional magnetron elements similar to those utilized in theforegoing figures and having the same function are identically labeledand the discussion is not repeated.

The relatively large rectangular piezoelectric sandwich or actuator 70includes first and second thin layers of piezoelectric material 71 and72, a middle conductive layer or electrode 73 and two outer conductivelayers or electrodes 74 and 75. The foregoing layers are aflixedtogether to form a physically integral thin flexible element. As isapparent, the dimensions of this element are exaggerated for purposes ofillustration. The relatively large rectangular shaped piezoelectricbimorph actuator '70 is mounted by two spaced bearing members 76 and 77located at the respective ends of the elongated rectangular bimorph.Each bearing includes supports 78 and 79 which restrain horizontalmovement of the ends of the piezoelectric bimorph actuator, but whichallows limited vertical or reciprocating movement of the ends of bimorphcaused by flexure of the bimorph at its center.

A coupling or linking means 80 connects any movement at the center ofbimorph actuator 70 to the movab e wall 90 of resonant output cavity 17,This coupling member 80 includes a plurality of rods 81, 82, and 83. Thefirst rod 81 is connected between the center of bimorph by clamplikebearings 84 and 85, to a linking members 86. Rod 81 is hollow, and aguide member 87, mounted in the pole piece 9 supports and guides themovement of rod 81. The other rods 82 and 83 extend through openings inflange portion 10 and are coupled to linking member 86 and to themovable cavity wall 90.

A tubular cylindrical wall 91 is connected to seal ring 6 and pole pieceflange 10. Connected to this wall is a washer shaped wall 92 joined towall 91 along its inner rim. Bearing members 76 and 77 which supportbimorph 70 are supported upon wall 92. A cuplike body portion has acylindrical side wall 94 attached to the outer perimeter of wall 92 anda circular disk shaped wall 95 joined to wall 94 with a seal ring 96 toclose the housing,

An electrical lead 97 is soldered to the outer electrode 74 ofpiezoelectric bimorph actuator 70 and extends from the interior to theexterior of the housing through a passage in wall 95. Supporting lead 97is a glass bead 98, which is itself suported by a flared tube 99connected to the disk shaped Wall 95. An electrically conductive helicalspring 100 is interposed between portions of electrical lead 97 to allowthe lead to follow the move ments of the bimorph, while providingminimal restraint. A like electrical lead is soldered to the middleelectrode 73 piezoelectric bimorph actuator 70, located immediatelybehind the lead 97 and is not visible in this cross-section. Access ofthis electrical lead is provided by cutting a pas sage through electrode74 and the piezoelectric layer 71. The bearings 78, preferred topreviously, are constructed of insulator material, and the secondbearings 79 are constructed of conductive material. Thus, a thirdelectrical connection is made between the electrode 75 of bimorph 70 towall 92 of the magnetron housing in lieu of another electrical lead.

Since the two ends of the bimorph actuator are restrained, the bimorphactuator warps or flexes at its center upon application of a sweepvoltage to the leads. This motion of bimorph actuator 7 is transmittedto rod 81. From rod 81, this motion is transmitted through the linkingmember 86 to rods 82 and 83; hence, to movable wall 90. As the positionof movable wall 90 is varied, the frequency of resonance of the resonantoutput cavity 17 is accordingly changed.

FIGURE shows an embodiment of the invention in which the motion aplurality of mechanically coupled bimorphs 110 is transmitted to amovable wall 116 of resonant output cavity 17 through a mechanicalcoupling or linkage assembly which extends from the exterior of theevacuated interior. The construction of this embodiment allows thebimorphs to be placed outside the evacuated regions of the magnetronwhere they are more easily excessible to adjust or substitution. Theconventional magnetron elements are labeled identically to thecorresponding elements in the foregoing figures. Insofar as they arealready discussed in the foregoing description, the description of theseelements is not repeated.

Each of the rectangular shaped piezoelectric bimorph actuators includesa first and second thin layer 111 and 112 of piezoelectric material suchas barium 'titanate a middle conductive layer or electrode 113 and twoother conductive layers or electrodes 114 and 115. The foregoing layersare aflixed together to forma physical integral thin flexible element.As is apparent, the dimensions of this element are exaggerated forpurposes of illustration.

The mechanical linkage assembly 117 coupling the bimorph assembly to themovable wall includes a first rod 118 which extends from the exterior tothe interior of the magnetron housing. An enlarged cuplike end portion119 of this rod is surrounded by and connected with a second linkage120. A hollow stem extension portion 121 protrudes .from within thecuplike portion 119. A guide member 122, mounted to-pole piece 9,extends within the hollowed stem portion of stem extension 121 toprovide a guide and support for the linkage assembly 117. A

second linkage 123 is coupled to the first linkage byone or more rods124. Linkage 123 in turn is coupled to the washer shaped movable wall116 with one or more rods 125 extending through openings in the polepiece flange 10. Rod 125 supports the movable washer shaped wall 116 ofresonant output cavity 17 for reciprocating movement.

The housing includes a washer shaped disk wall 126 sealed at its outerrim to a cylindrical wall 127 by a combined support and seal ring 128.Rod 118 extends from the housing exterior through the center opening ofwasher. shaped wall 126 into the inner portion of the A first bellows130 is connected at one end to a washer shaped flange 131 itselfconnected to disk wall 126 surrounding the opening therethrough andthrough which rod 118 projects into the formed chamber. The other end ofbellows 130 is connected to a washer shaped flange 132 attached to andsurrounding the cuplike portion 119 of rod 118. This bellows isconstructed of thin metal which is impervious to air. A second bellows133 is sealed at one end to a washer shaped flange 134 that is connectedand sealed along its inner rim to a portion of guide member 122. Theother end of bellows 133 is sealed to another flange 135 that is in turnsealed around the cuplike end portion 119 of rod 118 to enclose thestern portion 121 of rod 118 within the bellows. These bellows arevacuum tight but because of the accordionlike action, they allow motionfrom rod 118 to be transmitted from the exterior to the interior of theevacuated magnetron housing. As opposed to the use of a single bellows,the use of two bellows and openings 136 and 137 in the cuplike member119 permits equalization of air pressure on either side of the cuplikemember. This permits the rod 118 to reciprocate more linearly in eitherdirection than otherwise.

The exemplary construction of this embodiment shows six rectangularshaped piezoelectric bimorph actuators 110 mechanically clamped andspaced between insulating spacers 138 at one end in two stacks of threebimorphs. A bolt 139 and washer 140 serves to clamp the outer end ofeach stack to the rim 129. The inner ends of the bimorphs are clampedand spaced between insulating spacers 141 attached to the rod 118.Insulating spacers 141 are clamped between two spaced rim portions, 142and 143 of rod 118. A bolt 144 secures the clamping action. Bearingmembers 145 are contained in grooves 146 formed in each of theinsulating spacers 141 to allow some movement of clamped bimorphactuator. In addition, the bearings are of a conducitve metal 13 whichthus contacts each of the outer electrodes 114 and 115 of the bimorphactuators. Electrical leads, not illustrated, are attached to thesebearings for connection to a-source of sweep voltage.

The center electrode 111 of each bimorph actuator extends beyond theinsulators 138 to permit attachment of an electrical lead also connectedto the sweep voltage source. The application of a sweep voltage to thoseleads causes the flexure of. the bimorphs at their free ends, in thisillustration the ends connected to the movable rod118. This creates aforce sufficient to depress rod 118. The movement of rod 118 isaccordingly transmitted to the movable wall 116 by rod 125, link 123,rod 124, link 120, cup portion 119, and the rod 118, while the bellows130 and 133 move with rod 118 in accordionlike fashion. Any change inposition of the movable cavity wall 116 causes a change in the frequencyof resonance of the resonant output cavity 17.

FIGURE 6 shows the tunable magnetron structure incorporating anotherembodiment of the present invention. 'Insofar as the elements aresimilar to the structure of FIGURE 3, they are identically labeled, andsince previously described in detail, reference is made to that previousdescription. The construction of Washer shaped piezoelectric bimorphactuator 25 utilized to position a washer shaped movable wall 54 closingthe resonant output cavity 17 and forming a tuner therewith is identicalto that used in FIGURE 3. Therefore reference is made to thatdescription.

The piezoelectric bimorph actuator is mounted along an inner rim to amovable sleevelike member 150 by two clamping members 151 and 152fastened to sleevelike member 150 while the outer rim of thepiezoelectric bimorph is free to flex. Movable sleevelike member 150 isconnected to a linkage 153, which in turn is connected to a rod 154 thatextends through an opening in the flange portion of pole piece 9. Rod154 is connected to another link 155. A cylindrical wall 156 is sealedto pole piece flange 10 and seal ring 6 to form a chamber. A disk shapedend wall 157 is fastened to the cylindrical wall 156 by a thin metalbellows 158 and at the other end to a groove in cylindrical wall 156.This permits end wall 157 to move relative to cylindrical wall 156. Apiston or rod 159 is connected to link 155 fitting within a circulargroove on link 155. A cylindrical hollow rod 160 is connected betweenthe disk wall 157 and link 155,. fitting within a circular groovetherein. Piston 159 extends through disk wall 157 for connection withany of the heretofore known mechanical or electromechanical tuneractuator mechanisms or plunger positioner, as variously termed,symbolically shown by the rectangle 161 located outside the magnetronhousing. The bellows 158 permits the coupling of a driving movement frompositioner 161 and rod 159 to the link and rod elements located withinthe evacuated interior of the magnetron by expansion and contraction inaccordionlike fashion with the movement of rod 159.

External control or sweep voltages are applied to the electrodes of thebimorph 25 over electrical leads extending from within the magnetronhousing to the exterior. An electrical lead 162 is soldered to middleconductor 38 of the piezoelectric bimorph actuator 25. This lead extendsthrough an insulator 163 within an opening through flange portion 10 tothe lower portion of magnetron housing. An insulator 164 is supportedwithinan opening that extends through the cylindrical side Wall 156 by atubular support 165. An electrical lead 166 of larger diameter than lead162 extends through insulator 164 from the exterior to the interior ofthe housing and is connected with lead 162. A helical conductive spring167 is connected in series with lead 162 to allow the lead to yield withthe motion of the tuner which prevents the electrical lead from imposingany substantial restraint upon the movements of the piezoelectricbimorph 25. A second electricallead, not visible in. the sectional viewof FIG- URE 6, is similarly coupled to the outer conductive layer orelectrode 30 of the piezoelectric bimorph actuator 25, extending throughthe magnetron housing in the same manner as electrical leads 1'62 and166. That second electrical lead is located immediately behind theillustrated electrical leads and has similar accompanying structure, butis not visible in the section of the magnetron illustrated in FIGURE 5.The third conductive layer or electrode 29 of the bimorph tuner iselectrically grounded to the conductive magnetron housing by theconductive clamp ring 152, support 150, the conductive linkage 153,through rod 154, linkage 155, rod 160, wall 157, bellows 158 to theconductive wall 156 of the magnetron housing. This forms a thirdconductive path, used in lieu of a third electrical lead.

The external positioning or tuning mechanism 161 is used for setting theinitial position of movable cavity wall 54; and hence, the initialfrequency of resonance of resonant output cavity 17. The piezoelectricbimorph actuator 25 coupled to movable wall 54 provides additionalmovementaof the movable wall as desired to change the frequency ofresonance of cavity 17. Moreover, the actuator 25 can provide a periodicsweep movement of wall 54 at a very fast speed to rapidly tune or sweepthe cavity 17 through a bandwidth of frequencies about the initialfrequency. Alternatively, the external positioning or tuning mechansm161 reciprocates rod 159 to provide a periodic sweep movement of cavitywall 54 to tune the resonant output cavity 17 over a predetermined widebandwidth of frequencies at sweep rates low relative to the sweep ratesprovided by the piezoelectric bimorph actuator =25 while the bimorphactuator simultaneously reciprocates the cavity wall at a faster sweeprate over a smaller bandwidth. Thus, a very fast sweep rate of tuning ordither over a small bandwidth of frequencies is superimposed upon alower sweep rate of tuning over a larger bandwidth of frequencies. It isapparent that while the tunable magnetron embodied in FIGURE 6incorporates the piezoelectric tuner construction used in FIGURE 3,other forms thereof such as that illustrated in FIGURES 1 and 2 may belikewise modified to be carried upon the sleeve 150.

:Moreover, it is apparent that the details of any conventional externalplunger positioning member or tuner may be utilized to carry thepiezoelectric actuator 25 and movable wall 54 forming the tuner, andthat the invention embodied in this figure is not limited to theconstructional details found therein.

Each of the foregoing embodimentsof the invention contain manyconventional elements and utilizes conventional mechanical assemblytechniques known to those of ordinary skill in the art. Insofar asthesetechniques are not necessary to the understanding oftheimprovements disclosed in this application, they are not discussed.As is apparent, the tunable magnetrons disclosed in this application arein the complete construction mounted within a permanent magnet, andcontain a socket assembly mounted to the housing for making electricalconnection with the power supplies necessary to providethe magnetronanode, cathode, and filament with operating voltages. This isconventional in the prior art and is not illustrated. Likewise, forproviding operation of the piezoelectric tuner, a conventional source ofsweep voltage is connected between the appropriate electrical leadspreviously described. Moreover, in the event that a layer. of thepiezoelectric material is utilized to generate a tracking voltagerepresentative of the frequency to which the tuner is in resonance, asuitable indicator such as one oscilloscope or a control circuit isprovided in the customary manner.

In each of the foregoing embodiments, it is apparent that the inventionaffords the piezoelectric elements substantial protection from exposureto the microwave energy appearing in the resonant cavity, which cancause heating. In each of the foregoing embodiments, the piezoelectriclayers are isolated from the microwavefieldby the conductive wallforming the movable boundary of the cavity which reflects microwaveenergy incident thereupon. This protection is equally afiorded in theembodiment where the movable wall is connected to all points of theadjoining piezoelectric layer, and is, in fact, the electrode depositedupon the piezoelectric layer which performs the additional function ofacting as a cavity wall. Although there is some clearance between thewalls of the magnetron and the movable wall in order to allow the backand forth movement of the piezoelectric bimorph, this clearance isrelatively small as compared to the wavelength of the dominant modepresent in the microwave cavity, and therefore, acts as a very largeimpedance to prevent access of microwave energy to the piezoelectricbimorph elements of the tune-r located in the rear portion of the formedchamber. Thus, as compared to other types of tuners composed ofrelatively lossy ceramic materials, such as the ferroelectric type,which are directly exposed to high power microwave fields, a substantialadvantage accrues. Because the piezoelectric elements are elfectivelyisolated from microwave fields, the lossy material is not heated nor arethe brazing alloys holding the bimorph together heated which encouragesthe emission of vapors that might either eventually spoil the Vacuum orotherwise change the operating characteristics of the magnetron.

As is apparent, a microwave cavity incorporating the invention may beadapted to and be used with various types of microwave frequency devicessuch as electron discharge devices. As is known, many electron dischargedevices are utilized as oscillators. However, the type of oscillatorycircuits used depends upon the construction or type of electrondischarge device or microwave tube considered. Insofar as some type ofmicrowave cavity is utilized as the tuning mechanism for the tubes, themicrowave tuner of the present invention is of utility. Conventionalmagnetrons, which utilize a plurality of tightly coupled anoderesonators, open on three sides, are also tunable by the simultaneouspositioning of a wall at each of the anode resonators to one of theresonator openings. In such instance, the utility of the instantinvention is readily apparent. Moreover, in each of the foregoingembodiments, the piezoelectric bimorph tuner is of a two piezoelectriclayer sandwich construction. While this is preferable, it is apparentthat the invention can include a piezoelectric tuner having more thantwo piezoelectric layers.

Of course it is to be understood that this invention is not restrictedto the particular details as described above, as many equivalents willsuggest themselves to those skilled in the -art.'The foregoingembodiments, it is understood, are presented solely for purposes ofillustration and are not intended to limit the invention as defined bythe breadth and scope of the appended claims.

What is claimed is:

1. In a coaxial magnetron tunable at high rates which.

includes in a housing, a'cathode, an anode surrounding said cathode,said anode including an outer wall and a plurality of anode resonatorssupported adjacent to and-'1;

spaced about said cathode; a resonant output cavity surrounding saidanode, said cavity defined by the space between conductive walls whichincludes the outer wall of said anode, and a movable conductive wall,said movable conductive wall being movably mounted for changing the sizeof said resonant output cavity; said outer wall of said.

located outside said output cavity and being connected by 1 a firstconnecting means to said movable conductive wall for changing theposition of said movable wall asa function of the magnitude of anapplied control voltage and for generating a position representativevoltage as a func- 16 tion of the position of said movable wall, andelectrical circuit means connected to said piezoelectric bimorph meansadapted to convey control voltages to said piezoelectric bimorph meansfrom a source of control voltage and adapted to convey a positionrepresentative voltage generated by said piezoelectric bimorph means toa monitoring or control means. i

2. The invention as defined in claim 1 wherein said anode includes acylindrical inner wall, a plurality of vanes symmetrically connected atone end to and spaced about said inner wall extending radially inwardfrom said cylindrical inner wall within a predetermined distance of saidcathode, wherein each one of said plurality of anode resonatorscomprises the space between adjacent vanes; and wherein said resonantoutput cavity includes an outer cylindrical housing wall; and whereinsaid movable conductive wall is annular shaped to conform to the spacebetween said outer anode wall and said outer housing wall.

3. The invention as defined in claim 2 wherein said piezoelectricbimorph means is annular shaped.

4. The invention as defined in claim 3 further comprising: support meanswithin said housing connected to said piezoelectric bimorph and to saidhousing for tfixing the position of a portion of said piezoelectricbimorph while allowing the other portions thereof freedom to flex.

5. The invention as defined in claim 4 wherein said first connectingmeans comprises a metallurgical bond between said movable wall and saidpiezoelectric bimorph means whereby the movable wall is integral withsaid piezoelectric bimorph means.

6. The invention as defined in claim 4 wherein said first connectingmeans connecting said piezoelectric bimorph means to said movable wallcomprises a thin annular strip.

7. The invention as defined in claim 6 wherein said thin annular stripfurther comprises a bent over lip portion integral with said movablewall, and a groove at the juncture of the lip portion and said movablewall.

'8. The invention as defined in claim 2 wherein said first connectingmeans connecting said piezoelectric bimorph means to said movable wallcomprises a mechanical rod coupling means.

9. The invention as defined in claim 8 wherein said mechanical couplingmeans further comprises a first rod, a movable plate, and a plurality ofsecond rods; and wherein said second rods are connected between saidmovable wall and said plate at spaced locations; and said first rod isconnected between said piezoelectric bimorph means and said plate.

10. The invention as defined in claim 9, wherein said mechanicalcoupling means connected between saidpiezoelectric bimorph means andsaid movable wall further comprises, a movable rod means extendingthrough an. opening in said housing, and a bellows surrounding a.-

portion of said rod means and connected at oneend to the housingsurrounding the opening and at another end to a portion of said rodmeans to seal said opening.

11. The invention as defined in claim 10 further comparising a secondbellows means surrounding a second portion of said rod means at one endand to a second location on said housing at another end.

12. In a tunable electron discharge device tunable at a very high ratewhich includes a microwave cavity having a plurality of conductive wallsincluding a movable conductive wall located within an evacuated portionof a discharge device housing; positioning and tracking. means connectedto said movable wall for positioning saidmovable wall; said positioningand tracking means comprising: piezoelectric bimorph means including inathinfiexible physically integral sandwich; a first layer ofpiezoelectric material; a second layer of piezoelectric material; amiddle layer of conductive material separating said first and secondpiezoelectriclayer; a first outer layer of conductive material on the,outside of said first layer of piezoelectric material; and, a secondouter layer ofconductive material on the outside of said second layer ofpiezoelectric material; first electrical circuit means being adaptedforconnection to an external control signal source and connected betweensaid middle and first outer layer of conductive material for applying acontrol signal from an external control signal source across said firstpiezoelectric layer to position said movable wall, and second electricalcircuit means being adapted for connection to a tracking device andconnected between said middle and second outer layer of conductivematerial for conveying a position representative signal generated bysaid second piezoelectric layer.

13. The invention as defined in claim 4 wherein said support means ismovably mounted, and further comprising, external positioning meansconnected to said support means for moving said support means, wherebythe movable wall is moved at a first rate by said external positioningmeans and at a dither second rate higher than said first rate by saidpiezoelectric bimorph means.

14. In a coaxial magnetron having an annular output cavity resonatorbounded on one side by a movable metallic wall, a piezoelectric bimorphmeans attached to said movable wall responsive to applied controlvoltages for varying the position of said movable wall to change theresonant frequency of said cavity and for generating a voltage as afunction of the position of said movable wall; first electric circuitmeans connected to said piezoelectric 18 bimorph means for receivingapplied control voltages from a source and conveying said controlvoltages to said 8 piezoelectric bimorph means and second electriccircuit means connected to said piezoelectric bimorph means for.conveying a position representative voltage generated by 1 saidpiezoelectric bimorph means to an external monitoring or control means.

References Cited 20 HERMAN KARL SAALBACH, Primary Examiner S. CHATMON,1a., Assistant Examiner US. (:1. X.R. 310 s; 315 39. 61, 39.77; 331 90,155

